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Pohutukawa stem-gall wasp - Quadrastichodella sp. (Pohutukawa)

By N A Martin (2019)

Classification

Phylum:
Arthropoda
Class:
Insecta
Order:
Hymenoptera
Superfamily:
Chalcidoidea
Family:
Eulophidae
Subfamily:
Tetrastichinae
Scientific Name:
Quadrastichodella sp. (Pohutukawa)
  • Top view of an adult female Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae). Image: Tim Holmes © Plant & Food Research
    Top view of an adult female Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae). Image: Tim Holmes © Plant & Food Research
  • A old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
    A old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
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Common Names

Pohutukawa stem-gall wasp
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Taxonomic Notes

This unnamed gall wasp has been placed in the genus, Quadrastichodella, but when it is examined in more detail during its formal description and naming, it may be found to better fit another genus. All other known species of Quadrostichodella are Australian. At least two of these have been accidentally introduced to New Zealand and are associated with Eucalyptus and Tristaniopsis (water gum) respectively, both in the myrtle family (Myrtaceae) like pohutukawa. The pohutukawa stem-gall wasp is the first endemic New Zealand species to be recognised.

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Biostatus and Distribution

This endemic wasp has only been found in a few places of along the East and West coast of the Auckland Region. The gall wasp induces galls in the stems of Pohutukawa, Metrosideros excelsa (Myrtaceae). The stem galls with their distinctive exit holes were first found in 2003.

Conservation status: Unknown.

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Life Stages and Annual Cycle

Galls of the Pohutukawa stem-gall wasp have only been examined in the summer and winter when larvae and pupae were found. Adults have only been reared in the winter, but probably emerge at other times. The annual cycle of the wasp has not been adequately studied. It may have one extended generation per year or several generations. Eggs are probably laid into young new seasons stems in late spring or early summer. They may also be laid into a green gall. The new gall may form as a result of the eggs being inserted or as a result of larval feeding. Each larva, of which there are several per gall, forms a ‘cell’ in which it lives and feeds. The pupa is formed in the cell. The adult hatches from the pupa in the cell and when its body has hardened, it chews its way out of the gall, leaving a distinctive exit hole. The male and female adults find each other and mate.

Adult wasps
The adult female wasps are about 2 mm long. The body is dark brown to black. The base of each leg is black and the rest of the leg is mid brown. Like a typical wasp, it has three pairs of legs, a pair of antennae on its head and two pairs of wings. The female abdomen has a pointed ovipositor at the tip and which is visible on the underside.

Eggs, larvae and pupae
Female wasps lay groups of eggs in current season stems. The eggs may be inserted on one side or on all side of the stem. The larva hatches from the egg and it chews the gall tissue which develops into a hollow cell in which the larva lives and feeds. The legless larva has darkly coloured tiny jaws with which it eats the gall tissue. There are several larval instars (stages). The larva moults, or changes skin, as it gets larger. When it is fully grown the larva moults into a pupa that stays in the cell as it transforms to the adult.

  • Top view of an adult female Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae). Image: Tim Holmes © Plant & Food Research
    Top view of an adult female Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae). Image: Tim Holmes © Plant & Food Research
  • Top view of an adult female Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae). Image: Tim Holmes © Plant & Food Research
    Top view of an adult female Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae). Image: Tim Holmes © Plant & Food Research
  • Underside of an adult female Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae). Image: Tim Holmes © Plant & Food Research
    Underside of an adult female Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae). Image: Tim Holmes © Plant & Food Research
  • A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
    A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
  • A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) that has been cut to expose the cells in which the larvae live. Image: Nicholas A. Martin © Plant & Food Research
    A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) that has been cut to expose the cells in which the larvae live. Image: Nicholas A. Martin © Plant & Food Research
  • A section through stem gall in Pohutukawa, Metrosideros excelsa (Myrtaceae) induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the way the larval cells are on one side of the stem. Image: Nicholas A. Martin © Plant & Food Research
    A section through stem gall in Pohutukawa, Metrosideros excelsa (Myrtaceae) induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the way the larval cells are on one side of the stem. Image: Nicholas A. Martin © Plant & Food Research
  • A dissected stem gall in Pohutukawa, Metrosideros excelsa (Myrtaceae) induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the cut open cell with a larva inside. Image: Nicholas A. Martin © Plant & Food Research
    A dissected stem gall in Pohutukawa, Metrosideros excelsa (Myrtaceae) induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the cut open cell with a larva inside. Image: Nicholas A. Martin © Plant & Food Research
  • A dissected stem gall in Pohutukawa, Metrosideros excelsa (Myrtaceae) induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the cut open cell with a larva inside and the black head of a wasp in the adjacent cell. Image: Nicholas A. Martin © Plant & Food Research
    A dissected stem gall in Pohutukawa, Metrosideros excelsa (Myrtaceae) induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the cut open cell with a larva inside and the black head of a wasp in the adjacent cell. Image: Nicholas A. Martin © Plant & Food Research
  • The tail end of a larva of the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in the opened cell. Image: Nicholas A. Martin © Plant & Food Research
    The tail end of a larva of the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in the opened cell. Image: Nicholas A. Martin © Plant & Food Research
  • The underside of a larva of the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the dark tips of the jaws in the head. Image: Nicholas A. Martin © Plant & Food Research
    The underside of a larva of the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the dark tips of the jaws in the head. Image: Nicholas A. Martin © Plant & Food Research
  • A dissected stem gall in Pohutukawa, Metrosideros excelsa (Myrtaceae) induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) with cut open cells with a larva (left) and pupa (bottom centre). Image: Nicholas A. Martin © Plant & Food Research
    A dissected stem gall in Pohutukawa, Metrosideros excelsa (Myrtaceae) induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) with cut open cells with a larva (left) and pupa (bottom centre). Image: Nicholas A. Martin © Plant & Food Research
  • A larva (left) and pupa (bottom centre) of Pohutukawa stem-gall wasps, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in cut open cells of the stem gall. Image: Nicholas A. Martin © Plant & Food Research
    A larva (left) and pupa (bottom centre) of Pohutukawa stem-gall wasps, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in cut open cells of the stem gall. Image: Nicholas A. Martin © Plant & Food Research
  • Pupa of Pohutukawa stem-gall wasps, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in cut open cell of the stem gall. Image: Nicholas A. Martin © Plant & Food Research
    Pupa of Pohutukawa stem-gall wasps, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in cut open cell of the stem gall. Image: Nicholas A. Martin © Plant & Food Research
  • A pupa of Pohutukawa stem-gall wasps, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) removed from its cell in the stem gall. The red dot is the developing eye. Image: Nicholas A. Martin © Plant & Food Research
    A pupa of Pohutukawa stem-gall wasps, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) removed from its cell in the stem gall. The red dot is the developing eye. Image: Nicholas A. Martin © Plant & Food Research
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Recognition

Gall wasps (Hymenoptera) require specialist skills for their identification. However, the presence stem galls with tiny exit holes on Pohutukawa, Metrosideros excelsa (Myrtaceae) allows the presence of the Pohutukawa stem-gall wasp to be recognised. Slightly larger exit holes are made by weevils whose larva tunnels under the bark of young stems. The weevils exit holes are larger, close to 1 mm diameter.

Young galls without exit holes (because the wasp larvae and pupae are still developing, and no adults have emerged) could be mistaken for similar looking stem galls that are induced by scale insects. If identification of the gall is required and scale insects are not present, dissection is required to confirm the identity of the gall former. Galls made by scale insects don’t have the cells for the larvae and pupae.

  • A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
    A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
  • A old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
    A old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
  • A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) that has been cut to expose the cells in which the larvae live. Image: Nicholas A. Martin © Plant & Food Research
    A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) that has been cut to expose the cells in which the larvae live. Image: Nicholas A. Martin © Plant & Food Research
  • An old woody stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) that has been cut to expose the old cells in which the larvae lived. Image: Nicholas A. Martin © Plant & Food Research
    An old woody stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) that has been cut to expose the old cells in which the larvae lived. Image: Nicholas A. Martin © Plant & Food Research
  • Exit hole made by an adult Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in its gall on a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Image: Nicholas A. Martin © Plant & Food Research
    Exit hole made by an adult Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in its gall on a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Image: Nicholas A. Martin © Plant & Food Research
  • Exit holes made by an adult Pohutukawa stem-gall wasps, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in thier gall on a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Image: Nicholas A. Martin © Plant & Food Research
    Exit holes made by an adult Pohutukawa stem-gall wasps, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae) in thier gall on a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae). Image: Nicholas A. Martin © Plant & Food Research
  • A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced a Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) and the exit hole of a weevil. Image: Nicholas A. Martin © Plant & Food Research
    A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced a Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) and the exit hole of a weevil. Image: Nicholas A. Martin © Plant & Food Research
  • A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced a Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) and the exit hole of a weevil. Image: Nicholas A. Martin © Plant & Food Research
    A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced a Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) and the exit hole of a weevil. Image: Nicholas A. Martin © Plant & Food Research
  • A cut stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) exposing the tunnel made by a weevil larva. The weevil exit hole was in a scale stem gall. Image: Nicholas A. Martin © Plant & Food Research
    A cut stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) exposing the tunnel made by a weevil larva. The weevil exit hole was in a scale stem gall. Image: Nicholas A. Martin © Plant & Food Research
  • A young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with galls induced by the Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note splits in the bark over the gall. Image: Nicholas A. Martin © Plant & Food Research
    A young stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with galls induced by the Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note splits in the bark over the gall. Image: Nicholas A. Martin © Plant & Food Research
  • An old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with galls induced by the Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note splits in the bark over the gall. Image: Nicholas A. Martin © Plant & Food Research
    An old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with galls induced by the Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae): note splits in the bark over the gall. Image: Nicholas A. Martin © Plant & Food Research
  • Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note splits in the bark over the gall. Image: Nicholas A. Martin © Plant & Food Research
    Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note splits in the bark over the gall. Image: Nicholas A. Martin © Plant & Food Research
  • Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note splits in the bark over the gall and the wasp exit hole in the scale. Image: Nicholas A. Martin © Plant & Food Research
    Pōhutukawa button scale, Lecanochiton actites (Hemiptera: Coccidae) in a depression in the gall induced in a stem of Pohutukawa, Metrosideros excelsa (Myrtaceae): note splits in the bark over the gall and the wasp exit hole in the scale. Image: Nicholas A. Martin © Plant & Food Research
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Natural Enemies

No natural enemies of the Pohutukawa stem-gall wasp are known.

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Host Plants

The Pohutukawa stem-gall wasp has only one known host plant, Pohutukawa, Metrosideros excelsa (Myrtaceae). Laying eggs into young stems and/or feeding by larvae induces the stem to swell and form the gall.

  • A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
    A stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
  • A old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
    A old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
  • An old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
    An old stem of Pohutukawa, Metrosideros excelsa (Myrtaceae) with a gall induced by the Pohutukawa stem-gall wasp, Quadrastichodella sp. (Pohutukawa) (Hymenoptera: Eulophidae): note the three exit holes made by adult wasps. Image: Nicholas A. Martin © Plant & Food Research
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Information Sources

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/

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Suggested Citation

Martin NA. 2019. Pohutukawa stem-gall wasp - Quadrastichodella sp. (Pohutukawa). Interesting Insects and other Invertebrates. New Zealand Arthropod Factsheet Series Number 164. http://nzacfactsheets.landcareresearch.co.nz/Index.html. Date Accessed. ISSN 1179-643X.

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